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FERRO-MANGANESE AND SPIEGELEISEN

197

As impurities, ferro-silicon contains small quantities of carbon, manganese,
phosphorus, sulphur and, sometimes, calcium. Phosphorus is an injurious con-
stituent, the maximum allowable limit being 0-15-0-2%. The mean percentage
compositions of the commoner commercial forms are (Geiger) :

TABLE XV
Compositions of Ferro-silicons


	I
	II
	m
	IV
	V
	VI

Silicon       ....
	25-89
	29-66
	5I-80
	53-75
	51-20
	75-67

Iron     .....
	72-92
	72-99
	47-30
	45-09
	48-89
	23-01

Carbon .....
	0-5^
	
	O'^O
	
	
	

Manganese
	0-42
	0-56
	o-35
	o-ii
	o-37
	0-26

Sulphur     ....
	0-03
	o-oi
	0-O2
	0-005
	0-007
	o-oi

Phosphorus
	0-04
	0-30
	O-O4
	0-041
	0-04
	0-04

Aluminium
	—
	0-30
	—
	0-60
	0-17
	—

Chromium.
	—
	0-25
	-----
	—
	—
	—

Copper .....
	—
	—
	-----
	0-04
	—
	—

Lime    .....
	
	"
	-----
	0-05
	O-2I
	—

FERRO-MANGANESE  AND   SPIEGELEISEN

Ferro-manganese is usually obtained in the blast furnace from a mixture
of iron and manganese minerals, and serves for the de-oxidation of steels
and for the preparation of manganese steels and other special alloys. It
is slightly yellowish white, compact and with a granular structure inter-
sected, especially in the high percentage types, by bluish, iridescent,
acicular crystals.

Spiegeleisen is a form of white cast-iron very rich in manganese with
a peculiar lamellar structure and a sliining and sometimes iridescent surface ;
it has the same uses as ferro-manganese.

Analysis of these products may include, besides the determination of
the manganese, also those of the carbon, silicon, phosphorus, sulphur, etc.,
which are always present in the commercial products in larger or smaller
quantities.

1. Determination of the Manganese.—Numerous methods, gravi-
metric, volumetric and electrolytic, have been proposed for the determina-
tion of the manganese in ferro-manganese and manganiferous cast-irons
in general. The following will be described : Volhard's volumetric method
with the recent modifications introduced by Wolff, Schb'ffel and Donath,
and the electrolytic method.

(a} VOLUMETRIC DETERMINATION. This method is based on the fact that,
if a neutral solution of a manganese salt is treated with potassium per-
manganate, the whole of the manganese in it is oxidised at the expense of
the permanganate and precipitated, together with that contained in the
added permanganate, as the dioxide. The manganese present is calculated
from the amount of permanganate necessary for the oxidation.olybdate reagent.